This invention arose out of needs and concerns in the semiconductor processing industry regarding accurate determination of liquid volume in semiconductor processing fluid containers. The invention will, however, have other applications and is limited only by the accompanying claims.
The production of integrated circuitry in semiconductor wafers typically utilizes processing equipment in which various types of processing liquids are used to treat wafers and other substrates. The liquid utilized in such equipment is typically pumped from bottles or other containers into a processing area of the equipment where one or more substrates are received. Such liquids are typically provided to the processing area in precise volumes. One way of determining the volume of liquid supplied to a processor would be to precisely measure the deceasing volume of fluid within the respective containers resulting from operation of fluid delivery pumps. It further is desirable to monitor the volume of liquid within the various liquid containers to determine when such containers need to be refilled with more processing liquid.
In accordance with aspects of this invention, liquid level and change of liquid level within such containers is monitored or determined by acoustic reflection off the liquid level surface in the containers.